• Zaręba, Jan

Abstract

Thirteen new three-dimensional lanthanide(III)-2,5-thiophenedicarboxylate coordination polymers (Ln-CPs) with general formulas of [Ln2(2,5-TDA)3(DMA)2(H2O)]n (Ln-CPs 1–4) and [Ln2(2,5-TDA)3(DMA)2]n(Ln-CPs 5–13) (where 2,5-TDA2– = 2,5-thiophedicarboxylate dianion, DMA = N,N′-dimethylacetamide, and Ln = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), Yb (12) Lu (13)) have been synthesized solvothermally under two different temperature conditions in a DMA–H2O mixed solvent system. A structural analysis discloses that the four Ln-CPs 1–4 crystallize in the orthorhombic space group Pna21, whereas the eight Ln-CPs 5–8 and 10–13 crystallize in the triclinic P̅1 space group and Ln-CP 9 (Dy) adopts the monoclinic P2/c space group. The distinct crystal structures and coordination features indicate that lanthanide contraction, ancillary DMA molecules, and different coordination modes identified for 2,5-TDA2– play deciding roles in the self-assembly of Ln-CPs 1–13. The Ln(III) centers in compounds 1–13 exhibit three different coordination numbers, 9 (only 1; around La1), 8 (1–8 and 10–12), and 7 (4, 8, 9 and 11–13) with monocapped-square-antiprismatic, bicapped-trigonal-prismatic, and monocapped-trigonal-prismatic geometries, respectively. The title compounds display distinct 3D coordination frameworks with dinuclear (La2O15; for 1 and Ln2O14; for 2–4) SBUs and tetranuclear [Ln4O28] SBUs (for compounds 5–13). Variable-temperature magnetic susceptibility measurements were investigated for Ln-CPs 7–11 with an applied dc field of 1 kOe. The weak antiferromagnetic interaction and small ligand/metal mass ratio make Ln-CP 7 (Gd) a good candidate for low-temperature magnetic refrigeration with an impressive −ΔSmmax = 31.0 J kg–1 K–1 (63.6 mJ cm–3 K–1) at T = 2 K and ΔH = 7 T. Furthermore, the frequency and temperature dependences of the alternating current (ac) susceptibilities have been studied to explore the magnetic dynamics of Ln-CPs 8–10. Importantly, for compound 9 (Dy), the χ′m and χ″m curves and Cole–Cole plots at 2–6 K suggest the existence of slow magnetic relaxation behavior. Luminescence thermometry studies have been performed at 298–373 K for Ln-CPs 6 and 8. The Eu analogue (6) features a weak temperature dependence of luminescence lifetime (relative sensitivities of 0.43% K–1 and 0.34% K–1 at 298 and 373 K, respectively), whereas the Tb analogue (8) is a good lifetime-based luminescent thermometer with a constant relative sensitivity value of 1.35% K–1 in the investigated temperature range.

Topics

• impedance spectroscopy
• compound
• polymer
• susceptibility
• Lanthanide
• self-assembly
• space group
• luminescence